1. Field of the Invention
This invention relates to laser gyros of the four mode type.
This class of devices is described for example in a text entitled "Laser Applications" edited by Monte Ross, Academic Press, Inc. New York, N.Y. 1971 in which pp. 134 to 200 relating to "The Laser Gyro" are particularly to be noted.
It is well known that two counterrotating laser beams may be established in a ring type laser. When the ring laser is rotated about an axis perpendicular to its plane or passing centrally through the ring laser, the frequency of the oscillations are shifted, with the frequency of the beam travelling in the direction of rotation exhibiting a decrease, and the frequency of the beam travelling in the direction opposite to the rotation exhibiting an increase. The amount of rotation may be determined by detecting the beat frequencies between the counterrotating beams. Using a set of three laser gyros, this phenomenon may be used in inertial guidance systems to determine the rotation and the resultant orientation of an airplane or the like.
Four more laser gyros are known in the art, and they employ optical crystals and Faraday effect devices to shift the frequency of the laser beams. However, the biasing and detection schemes which have been proposed up to the present time have been unduly complex and have had high noise levels associated with them.
Accordingly, principal objects of the present invention are the simplification and reduction in noise of four mode multi-oscillator laser gyros.